Removal of Al, Fe and Si from complex rare-earth leach solution: A three-liquid-phase partitioning approach

Abstract

A new strategy was suggested to remove Fe, Al and Si impurities from rare-earth leach solution by controlling partitioning and selective enrichment of those impurities and rare earths in three-liquid-phase systems. Experimental results indicated that aqueous pH value and addition of water-soluble complexing agents or their mixtures into initial aqueous solution have significant influence on three-liquid-phase partitioning of Fe, Al, Si and rare earths. When only 1,10-phenanthroline was added, Fe and Si can be “filtered” into PEG-rich middle phase of three-liquid-phase system (Cyanex 272/PEG 2000/(NH4)2SO4–H2O) without affecting separation of heavy and light rare-earth ions in top organic and bottom salt-rich phase, respectively. Al remained in bottom phase. However, addition of EDTA and 1,10-phenanthroline promoted enrichment of Fe, Al and Si into PEG-rich middle phase, and almost all of rare earths were concentrated in salt-rich bottom phase. Those rare earths in salt-rich phase after removal of impurities can be further separated by another three-liquid-phase system of Cyanex 272/PEG 600/(NH4)2SO4–H2O. Heavy, middle and light rare earths, Yb, Eu and La, can be selectively enriched into different liquid phases. Therefore, separation of non-rare-earth impurities from rare earths, and then between light, middle and heavy rare earths can be achieved by two stages of three-liquid-phase partitioning. The present work highlights three-liquid-phase system can be a potential separation media for removal of Fe, Al, Si from complex rare-earth leach solution and group separation of different target metals into different liquid phases.